98 lines
6.0 KiB
Plaintext
98 lines
6.0 KiB
Plaintext
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| File Name : COMBRISK.ASC | Online Date : 01/15/96 |
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| Contributed by : InterNet | Dir Category : ECOLOGY |
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| From : KeelyNet BBS | DataLine : (214) 324-3501 |
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| KeelyNet * PO BOX 870716 * Mesquite, Texas * USA * 75187 |
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| A FREE Alternative Sciences BBS sponsored by Vanguard Sciences |
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| InterNet email keelynet@ix.netcom.com (Jerry Decker) |
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| Files also available at Bill Beaty's http://www.eskimo.com/~billb |
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Combined, Environmental Risks Deadly, Researchers Learn
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Acidic water and ultraviolet light in combination damage the embryos of frogs
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far more seriously when acting together than when acting separately, according
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to a laboratory study at the University of California, Santa Cruz. This
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finding has major implications for understanding environmental threats to many
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species.
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Researchers exposed the eggs of a common species of frog to various levels of
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acidity and UV-B radiation, the most harmful form of ultraviolet light. By
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themselves, even the most acidic water or the most severe UV-B radiation did
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not kill many embryos. But when the two environmental assaults were combined,
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as many as half of the eggs failed to hatch.
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Ecologists should look for similar interactions in nature as they try to
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explain why many populations of amphibians around the world are dying out, the
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study's authors say. Stresses such as habitat loss, a thinning ozone layer,
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acid rain, pesticides, disease, and global climate change may combine to wreak
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more havoc on frogs, toads and salamanders than any one factor could by
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itself. Indeed, some scientists now suspect that for any given group of
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amphibians in trouble, two or more such factors may interact synergistically -
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that is, the combined effects of the stresses are far greater than the sum of
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their individual effects.
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"People have been looking for a smoking gun to explain the amphibian die-offs,
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and there isn't just one smoking gun," says Michael Soule, coauthor of the
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study and professor emeritus of environmental studies at UCSC. "There's quite
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an armamentarium out there. We're just beginning to look at the interactions
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among these possible causes."
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The UCSC group published its work in the October 1995 issue of the scientific
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journal Conservation Biology. First author was biologist Leslie Long, who
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completed the study for her master's thesis in marine sciences. Coauthors were
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former UCSC undergraduate Loralei Saylor, now at the Arizona Department of
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Game & Fish, and Soule.
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"We're not trying to say that a combination of UV radiation and low pH is the
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answer for why a particular amphibian population is declining, or even that
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this is happening now in the field," says Long. "The main message is that
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synergisms can be important and are worth looking for. We may miss a lot if we
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only look at each factor in isolation."
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Another recent study supports Long's view. Ecologists Joseph Kiesecker and
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Andrew Blaustein at Oregon State University found that a synergism between UV-
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B radiation and a fungal disease can kill embryos of the Cascades frog and the
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western toad. The combined effects of ultraviolet light and infection by the
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fungus magnified the harm done to the eggs beyond the sum of the individual
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effects of each factor. The work appeared in the November 21 issue of the
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Proceedings of the National Academy of Sciences.
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In 1994, Blaustein's group also showed that UV-B light by itself can kill frog
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and toad embryos in the field. "Both our new paper and the Long paper show
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that we should look not just for single effects, but also for combinations,"
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Blaustein says. "We don't think low pH is a factor in Oregon, but it may
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interact with UV radiation in other parts of the country. UV is important
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here, but it doesn't play a big role in the tropics. There will not be
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a single global cause."
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For their study, Long and her colleagues used three levels of acidic water (pH
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readings of 6.0, 5.0, and 4.5) and three levels of ultraviolet light: no UV-B
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(as a control), a "normal" level for high elevations, and a level forecast if
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the ozone layer continues to thin. The team exposed several dozen eggs of the
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leopard frog, Rana pipiens, to one of the nine possible combinations of
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factors. About one-quarter of the embryos died under the conditions of lowest
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pH and moderate UV, while half died when subjected to the lowest pH and the
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highest UV. In all other treatments - including the lowest pH by itself and
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the highest UV by itself - at least 90 percent of the eggs hatched.
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Several caveats apply, the authors note. The highest level of UV-B radiation
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simulated a future earth with an ozone layer 30 percent thinner than it was in
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1979. The most acidic water had a pH of 4.5, a reading seen infrequently in
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nature. Further, the study considered only the lab effects of those factors on
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the eggs of one species. In the wild, each of the many species of amphibian
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would react differently at each stage of life to these and other stresses.
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Acid rain can send pH levels as low as between 4.6 and 5.4 in lakes in the
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eastern U.S., Canada, and Europe, research has shown. Other workers have found
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pH levels of 4.5 in northern California and 5.0 in the Rocky Mountains. In
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addition, surges of acidified water may occur in mountainous areas when snow
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melts in the spring. High-elevation frogs breed in that season - a time of
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year when UV radiation is near its peak, the UCSC team notes.
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Soule hopes to work with a molecular biologist to explore why the pH-UV double
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whammy harms the eggs. The team observed that embryos died when their egg
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membranes did not expand, a "curling defect" that trapped the growing tadpoles
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inside in tight coils.
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